1. Field of the Invention
The present invention relates to a display device, a driving method thereof, a display panel, and a camera. In particular, the present invention relates to a sampling device which samples a video signal (image signal), a display device which includes the sampling device, and a camera.
2. Description of the Related Art
Generating sampling pulses in a time series and extracting a signal at each time from data signals are executed in many kinds of signal processing devices. Here, to sample the signal corresponding to a predetermined pixel from video signals in a display device of displaying images is included in such a process.
In a case where the video signals are processed inside the display device, the time difference between a sampling signal (that is, the signal which is used for sampling) and a sampling-object signal (that is, the signal for which sampling is performed) occurs due to a propagation delay of a circuit. Here, a variation (or dispersion) occurs in such a delay time due to a change in characteristics of circuits provided inside the display device, a change in an environment, and the like.
Incidentally, when sampling is executed, if the timing of a sampling pulse (signal) and the timing of the sampling-object signal do not satisfy a predetermined relation, it is impossible to execute accurate sampling.
For this reason, it is necessary to adjust the timing of the sampling signal so as to be able to execute accurate sampling. More specifically, it is necessary to adjust and generate a phase for a reference clock signal of the sampling pulse so that the sampling pulse has optimum timing for the sampling-object signal when it is transmitted to a sampling circuit.
Japanese Patent Application Laid-Open No. 2005-004191 discloses a method of sweeping a certain range of phases of sampling pulses as detecting sampling outputs, and setting the phase of the maximum output as an optimum phase. In this method, to make the phase optimum, it is necessary to provide a circuit that measures the outputs and acquiring the maximum value.
Incidentally, when the sampling result is converted into the output, if a variation of input/output conversion characteristics occurs among the respective sampling circuits, the output acquired from the sampling result does not correctly reproduce the original data signal even if the sampling is accurately executed.
In the display device, a display data generation circuit for sampling the video signals and outputting the acquired signals as display data is one kind of, so-called, sampling devices. However, if the signal to be transmitted to the display device includes a variation which is not included in the input video signal, the display quality at the display device remarkably deteriorates.
United States Patent Application Published No. 2004/0183752 discloses, as a method of detecting and correcting characteristic variations of respective sampling circuits, a method of commonly connecting current outputs of the respective sampling circuits to make them as one current output, measuring the acquired current output by an external current measuring circuit, and then correcting a data signal based on the measured current output.
Thus, in the display device, the method of commonly connecting the sampling circuit outputs to the current measuring device is frequently used to correct the variation of the sampling circuit. In that case, it is necessary to provide the circuit for correcting the variation in addition to the above-described timing correction circuit, whereby the whole circuit constitution of the sampling device becomes complicated.